I have an auxiliary Titan fuel tank that I put in the bed of my 2017 SD 6.7L when we go long distances on vacation. It holds around 40 gallons. When my main tank gets low i press a button that pumps approximately 5 gallons from the aux tank to the main tank. The issue I have is the fuel gauge for the main tank takes forever to show the new fuel level. An hour or more. By that time as the gauge is getting lower I’m thinking do I run more in or wait? Sometimes if I stop the engine & restart it updates but when I’m on the road I don’t like to stop. Not a real big issue to be sure as I can add more from the aux tank at any time but I’d sure like to have it update quickly. Anyone else dealing with this? Thanks

 

Yup, fuel level sensor is super slow to change, when I open the valve on my aux tank, it can be almost an hour before it shows a change in level, then suddenly it jumps up.

 

Whenever I pour in 5 gallons of fuel into a tank that says it's at 0 fuel level, I shut the motor off, and when I start the vehicle the fuel gauge always reads... 1/8 to 1/4 or so... Do you shut the engine off...???

 

I am pretty sure he is talking about doing it as he goes down the road, not stopping.

 

Well if that is the way he is doing it he needs to stop and re-start to get a proper reading right away... JMO

 

Same thing for me when adding to the main tank from my auxiliary tank while moving. If filling the main tank at a fuel stop, and you leave the truck running the gauge goes up as you fill. Must be something in the fuel system that detects movement and doesn't allow the gauge to go up.

 

I could stop/restart the engine but that’s a bigger hassle than waiting it out or pressing the actuator for another 5 gallons what with pulling a fifth wheel & having to find a safe place to pull over. Anyway not a great big deal especially since I now know my gauge is functioning “normally”🤔

 

It's got to do with the volume rate of change and how the fuel pump's sending unit sees it - I believe they have it programmed to 'average' it out over an amount of time so the gauge isn't 'bouncing' around so much, but that's reset every time the key is cycled. A lot of what I'm about to say is guesswork that I seem to recall hearing previously, so take it with a grain of salt.

If you add fuel at the pump, that's pumping a LOT of volume in a very short amount of time, so even 5 gallons added like that is going to show up quickly. Adding fuel quickly is going to make 'waves' in the tank that the sending unit will definitely see, and it will adjust accordingly. It's approximately a 1" hose, it can move a LOT of volume in a short amount of time.

I'm guessing your transfer pump probably uses 1/4" or 3/8" hose, I'd be surprised if it's bigger than that. That transfer pump likely also doesn't flow very rapidly, I'd be surprised if it transfers that 5 gallons in anything faster than a few minutes. It's basically trickling into the tank, so you're not getting the 'waves' that a commercial fuel pump will create, so the fuel pump's sending unit is still 'averaging' its level over whatever amount of time.

A solution for OP might be to put a flow meter on his pump, so he KNOWS that it actually transferred fuel. If he doesn't get a reading then he'd know he didn't transfer fuel.